Heterophoria is defined as a latent strabismus that is detectable only with monocular vision. In binocular vision with both eyes, the latent visual defect is involuntarily compensated for by motor and sensory alignment of the two eyes via active muscle power. When binocular vision is disrupted and the direction of gaze of the two eyes can no longer be aligned, most people experience a slight divergence in the visual axes of the two eyes.
What is heterophoria?
When both eyes are aligned to a point in the distance, our motor and sensory positioning mechanisms of both eyes via the external eye muscles ensure that the two visual axes are exactly parallel. Without these positioning mechanisms, the image would otherwise be blurred or even double-imaged. When the distant point approaches us and we continue to fixate it with both eyes, both visual axes are gradually actively rotated inward by a few arc seconds and by several angular degrees at extreme proximity. If the active alignment of the visual axes fails to occur when a point in the distance is fixed, and thus also the motor adjustment mechanism of the eyes, a slight rotation of the visual axis of the non-active eye occurs in about 80 percent of people. De facto, this constitutes a slight strabismus. The deviation of the visual axis of the inactive eye can be slightly twisted inwards, outwards or upwards or downwards around all three spatial axes. Combinations of the misaligned or decoupled visual axes between inward/outward and upward/downward are also possible. Usually, heterophoria involves only a few arcseconds to a few angular degrees by which the visual axes deviate from parallelism.
Causes
Three possible causative complexes are held responsible as triggers and causative agents of heterophoria, according to which latent strabismus is named and classified. A distinction is made between static, accommodative, and neurogenic heterophoria. The static cause complex includes all anatomical components such as the orbit and the position and nature of the retaining apparatus of the eyeball. Accommodative heterophoria may be caused by refractive errors or by a specific form of farsightedness. Neurogenic factors for the development of heterophoria may consist in nervous transmission problems of visual impulses. A disturbed further processing of the signals in ganglia or in the CNS can also be a possible cause. This leads to a limited or completely failed “image processing”. Decreased neurological processing of neuronal impulses usually also leads to inability of sensory image fusion of both eyes.
Symptoms, complaints, and signs
In the vast majority of cases, heterophoria is mild. Errors in the nonparallelism of the two visual axes during accommodation to distance are corrected without symptoms by the motor-sensory adjustment mechanism in binocular vision. Only when heterophoria is more pronounced, the external eye muscles are so stressed by the active positioning mechanism that nonspecific symptoms appear. Some of the observed symptoms and signs may be, for example, the onset of headaches and blurred vision, because the unconscious positioning mechanism overstrains the outer eye muscles. In the case of even more pronounced heterophoria, dizziness, lack of concentration and increased sensitivity to glare may also develop. Typically, the signs and symptoms grouped under the term asthenopia do not appear until later in the day. This is most likely related to gradual fatigue of the external eye muscles.
Diagnosis and course of the disease
In normal cases, in which no symptoms of heterophoria occur, this type of defective vision remains undetected and without consequences. Only when increasing symptoms appear in each case during the course of the day is an examination and clarification in this regard recommended. Common devices used for the examination and differential diagnosis of all types of strabismus are the visual acuity projector, the haploscope and the much more complex phase difference haploscope.Latent refractive error of heterophoria usually does not show further progression because it often exists from birth due to anatomical peculiarities. In cases where it is acquired due to nervous diseases or due to diseases of the external eye muscles, the course depends on the further development of the underlying disease.
Complications
Heterophoria usually results in strabismus in the patient. The strabismus can affect children in particular, not infrequently leading to bullying or teasing. The patient’s quality of life is generally reduced and everyday life is made more difficult. It is not uncommon for heterophoria to cause dizziness, as the patient can only see out of focus. Due to the visual impairments, daily activities are also made more difficult and limited. Furthermore, in many cases headaches or so-called double vision or veil vision occur. Concentration also decreases due to the disease, which can have a negative effect on everyday life and school performance, especially in children. Many affected individuals feel dizzy and exhibit increased sensitivity to light. There are usually no particular complications associated with the treatment of heterophoria. Treatment is primarily through visual aids or surgery and does not lead to further complications. However, in most cases, the surgical procedures cannot be performed until adulthood, which is why children are still dependent on the visual aids.
When should you go to the doctor?
Heterophoria has no disease value in many people and does not need to be treated. Up to 80% of people live with a diagnosis of heterophoria and do not notice any limitations or discomfort in everyday life. Since they describe themselves as symptom-free, no medical care is needed in these cases. The visit to the doctor is only necessary as soon as disturbances of vision or other complaints occur. If double vision or blurred vision is seen, a doctor should be consulted. If the field of vision is perceived as blurred or unclear, it is recommended to consult a doctor. If the vision complaints increase in intensity or extent over time, an eye test should be performed immediately. If the general risk of accidents increases or there is an increase in misjudgement of distances, a visit to the doctor is necessary. If the familiar lettering on traffic signs can no longer be deciphered, this is an indication of reduced vision that should be investigated. In the case of other complaints such as headaches, a feeling of pressure in the head or burning eyes, these symptoms should be discussed with a doctor. If there are disturbances in concentration, increased irritability, or if fatigue sets in prematurely despite sufficient nighttime sleep, further examinations are advised to clarify the cause.
Treatment and therapy
For heterophoria requiring treatment, there are basically three different forms of therapy. Passive therapy may include the use of custom-made eyeglasses. The latent refractive error can be compensated in whole or in part by the spectacle lenses. This relieves the motor-sensory adjustment mechanism of the eyes, so that the typical symptoms of fatigue do not occur and the symptoms quickly disappear. In other cases, special vision training can already lead to success. This involves targeted eye muscle training, which is primarily used to train convergence, i.e. inward movements of the eyes (near accommodation) and the avoidance of double images. Among many other exercises, vision training also includes visual relaxation exercises. The third form of therapy consists of surgical intervention, which mainly involves corrections to the external eye muscles. The corrections are made in such a way that the visual axes of the two eyes are as parallel as possible in a relaxed state after the procedure. This relieves the eye muscles during distance accommodation, so there should be no more signs of fatigue.
Outlook and prognosis
The prognosis of heterophoria can be considered favorable. In many cases, spontaneous remission occurs after only a few hours. The patient often experiences no discomfort. The sensory stimuli are processed correctly in the brain despite the strabismus, so the affected person does not experience any impairment.The strabismus is noticed by people present, although the affected person does not experience any significant changes in vision at those moments. Often, a complete recovery is already given with sufficient night sleep. The eye is no longer able to present full functionality due to overexertion or overtiredness. After a restful sleep there is a regeneration of the disturbing factors and therefore subsequently the full functional capacity reappears. If the heterophoria was triggered by a heavy alcohol consumption, a complete regression is bound to the degradation process of the harmful substances from the organism. Consequential damage to the eye or a permanent disturbance of vision is not to be expected with heterophoria. Rather, the process of squinting is seen as an indication from the body of overstraining. It occurs in almost everyone throughout life and is not considered a cause for concern. If heterophoria occurs more frequently, the triggering cause should nevertheless be looked at more closely, as there is usually a need for fundamental action.
Prevention
Direct preventive measures that could prevent the development of heterophoria do not exist. The condition forms due to genetically determined mild abnormalities immediately after birth or it is acquired due to specific neuronal or muscular diseases. This means that only indirectly acting preventive measures are conceivable to minimize the risk of developing a corresponding muscular or neural disease.
Aftercare
Affected persons are primarily dependent on a rapid and, above all, an early diagnosis in the case of heterophoria, as this is the only way to prevent further complications or a further worsening of the symptoms. It is also not possible for the condition to heal on its own, so treatment must be carried out in any case. Further aftercare measures are usually not available to those affected. Parents in particular must recognize the disease in their children at an early stage and then seek medical attention immediately. In most cases, the symptoms of heterophoria are relatively well alleviated by wearing glasses. Those affected must wear their glasses or contact lenses permanently so that the defective vision is not exacerbated. Regular examinations and checks by an ophthalmologist are also very useful. In some cases, however, surgical intervention is necessary. After such an operation, the patient must rest and take care of his or her body. In this case, the patient should refrain from exertion or physical activities in order not to put unnecessary strain on the body. As a rule, heterophoria does not reduce the life expectancy of the affected person.
What you can do yourself
Heterophoria does not always require medical treatment. In the case of mild strabismus, targeted eye muscle training is often already sufficient. This special vision training is guided by a specialist and can be continued independently at home. Accompanying visual relaxation exercises are used, such as visual meditation or similar measures. If strabismus causes symptoms such as headaches or dizziness, it usually helps to close the eyes for a few minutes. If the symptoms are severe, herbal remedies can be resorted to. Headaches, for example, can be relieved by essential oils. Mineral clay can also reduce the throbbing and at the same time prevent dizziness. If concentration is poor, plenty of water should be drunk. A proven alternative from homeopathy is the remedy Belladonna, which can be taken in consultation with an alternative practitioner. If the symptoms increase, however, heterophoria must be treated surgically. In this case, the best self-help measure is to take it easy on the affected eye after the operation. According to the doctor’s instructions, special care products can be used to relax the irritated eye and prevent infection. If signs of inflammation become apparent, the responsible ophthalmologist must be informed.
